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UPSC » UPSC CSE Study Materials » NCERT Notes for UPSC 2025 » Stars

Stars

Celestial objects that produce their light are called stars. Constellations are groups of stars that form familiar shapes. Astronomical distances are measured in Light Years.

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Stars

Celestial objects include the stars, planets, moon, and various other sky things. Stars are celestial bodies that produce their light. The Sun is a star as well. The solar system comprises the Sun and the celestial bodies that rotate around it. Since other stars are millions of times further away than the Sun, we see them as mere twinkling points. Stars can also be seen throughout the day, but the intense sunlight obscures them. It appears that stars are moving from East to West. Even though it is in the direction of the Earth’s axis of rotation, the pole star seems to be motionless from Earth.

Light Year

  • It is the distance that light travels in a year. Large distances, such as the distance between stars, are best expressed in light-years.
  • Light travels at a speed of around 300,000 kilometres per second. As a result, the Sun’s distance from the Earth is approximately eight light minutes (150,000,000 kilometres).
  • Proxima Centauri is the next closest star. Alpha Centauri is approximately 4.3 light-years away (40,000,000,000,000 km).

Constellations

These are clusters of stars that resemble identifiable forms. The constellation’s form remains the same. They look to be moving from East to West in the sky.

  • A constellation has many stars, but we can only see the brightest ones with our naked eyes.
  • A constellation’s stars are not all at the same distance from one other. In the sky, they are just in the same line of sight.

Here’s the list of the major constellations:

Ursa Major (Saptarshi):

  • It’s also known as the Great Bear or the Big Dipper.
  • One can view it in the early hours of the night during the summer.
  • This constellation has seven notable stars.
  • It resembles a large spoon or a question mark. The spoon has three stars on the handle and four in the bowl.
  • According to legend, the Saptarshi, a group of seven sages, preserve the timeless knowledge of the Vedas and convey it to humans in each new age.
  • Saptarshi has been linked to seven well-known Indian sages throughout history. • Ursa Major can be used to find the Pole Star: Consider a straight line running through the two stars at Ursa Major’s end. Extend this imaginary line in the direction of the north. This route will lead to a faintly glowing star. The Pole Star is the brightest in the sky.                               
  • The Pole star does not move to Earth, whereas other stars and constellations wander from east to west. Ursa Major revolves around the Pole star because it also moves from east to west. In reality, it appears that all of the stars revolve around the Pole star.
  • The Pole Star is not visible from the southern hemisphere. Some northern constellations, like Ursa Major, may be inaccessible from the southern hemisphere.

Orion

  • It’s also known as the Hunter.
  • It can be observed in the late evenings during the winter.
  • The three centre stars represent Hunter’s belt.
  • The four bright stars appear to be in a quadrilateral formation.                   
  • The brightest star in the sky, Sirius, is close to Orion and is the brightest star in the sky. Consider a straight line travelling across the three centre stars of Orion to find Sirius. Take a look east along this line. This path will take you to a brilliant star. Sirius is the star.

Cassiopeia

  • It can be seen in the early hours of the night during the winter.
  • It resembles a skewed letter W or M.

Conclusion

Stars are astronomical bodies that produce their natural light. The Sun is a star as well. It is practical to describe star distances in light-years. The stars seem to be moving from east to west. Since it is near the planet’s rotational axis, the pole star seems to be motionless from Earth. Constellations are clusters of stars that resemble familiar shapes. The solar system is made up of eight planets and many asteroids, comets, and meteors. A satellite is a body that revolves around another body. Venus is the most visible planet in the dark sky. Jupiter is the solar system’s most giant planet.

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